Biological and Physical Conditions at a Newly Placed Gravel Bar Habitat in the Tombigbee River

摘要

A pool-riffle habitat was constructed in an abandoned channel of the Tombigbee River near Columbus, Miss. The habitat is located below a minimum flow release structure in Columbus Dam, which releases about 5 cu. m/sec surface water from Columbus Lake. The habitat was constructed with 24,000 cu. m of 2- to 80-mm gravel and consists of two 60-m-long riffle separated by a short pool. The gravel constricts the river channel, increases water velocity in the riffle to 50 cm/sec, and provides substrate for aquatic organisms. The riffle are 46 m long and 24 m wide with a maximum depth of 1 m. After nearly 2 years in place, the substrate has not armored, and bottom material is relatively unconsolidated. Colonization by invertebrates at the gravel bar was rapid. After 3 months, 19 to 21 taxa were identified, and estimated densities were 3,496 and 2,868 individuals sq. m Riffle I and II, respectively. The fauna was dominated by oligochaetes and chironomid larvae; both groups made up about 63 percent of the community. By October 1985, approximately 8 months after placement, more than 40 macroinvertebrate taxa had been identified at the site. Total density of macroinvertebrate was estimated at 11,094 and 9,646 individuals sq m at Riffle I and II, respectively. A total of 42 species were collected in the study area, 39 were found at the gravel bar, 25 were found in the river channel, and 16 were obtained in the flume. Unusual or rare species of fishes were periodically collected at the habitat.